Negative resistance characteristics have been attained by a complementary pair of FETs (field effect transistors) connected in series by their sources to each other and connected by their gates to the drain of the other as described in the article entitled "Synthesis of Electronic Bistable Circuits" by L. O. Hill, D. O. Pederson and R. S. Pepper, in IEEE TRANSACTIONS ON CIRCUIT THEORY, volume CT-10, 1963.
The device introduced in said article was formed with an n-channel FET and a p-channel FET connected in the abovementioned way, and was to perform a dynatron type negative resistance (.LAMBDA.shaped current-voltage)characteristic. Such negative resistance characteristic can be obtained by the aforementioned connection a complementary pair (a pair of opposite conductivity types) of depletion mode FETs, for instance, a conplementary pair of junction type FETs, a complementary pair of MIS (metal-insulator-semiconductor) type FETs or a junction type FET and a MIS type FET of the other conductivity type.
In general, such negative resistance devices are useful in switching, oscillation, amplification, memorying, etc. One of the most important uses of the device would be for integrated memories. In such integrated memories, in view of the density of the integration, the combination of the MIS type FETs is advantageous. However, since it is difficult to realize a p-channel FET in the depletion mode, it has been difficult to form the negative resistance device by means of a complementary pair of the MIS type FETs in monolithic a substrate. The reason of such difficulty is an that SiO.sub.2 which gate film is formed on an n-type Si substrate, while making the FET, the SiO.sub.2 film is usually contaminated by impurities such as Na.sup.+ ions, etc. Accordingly the SiO.sub.2 gate film becomes positively charged, and hence, electrons are accumulated at the semiconductor surface underneath the SiO.sub.2 gate film. Therefore it is easy to realize a p-channel FET of enhancement mode, but that of depletion mode is difficult.